TB Micro Flashcards
characteristics of mycobacterium tuberculosis
- aerobic, acid fast rods
- cell wall has mycolic acid = resistant to detergents and common abx; protects it from desiccation
- grows very slowly on culture
- facultative intracellular
TB: transmission, incubation period, virulence factor
- transmitted by inhalation
- incubates for 4-12 weeks
- virulence factors = cord factor; gives the bug its characteristic serpentine arrangement
what causes the tissue necrosis?
immune response
what are the symptoms of TB?
- mild fever, chest pain, fatigue, malaise, unintentional weight loss
- SWEATING especially night sweats
- PRODUCTIVE cough, sputum could be bloody
risk factors for TB
- poor nutrition
- drug users
- alcoholics
- crowded living conditions i.e. prison
- immunocompromised
- endemic areas = SE Asia, Sub-Saharan Africa, Eastern Europe
3 types of TB
- primary TB = initial case
- Secondary TB = reactivation of TB
- Disseminated TB = involves multiple systems AKA miliary TB
progression of TB
- inhalation of bacteria
- gets engulfed by alveolar macrophages
- the bug isn’t killed; it survives and multiplies
- attracts and activates more macrophages
- forms a tubercle/granuloma in lungs
- can remain dormant for years or decades; something triggers it to come out i.e. becoming immunosuppressed
how do the tubercles changes over time?
- starts as caseous lesion = cheese like consistency
- becomes Ghon complex = lungs & lymph nodes involved; calcified caseous lesion that shows up prominently on CXR
- then it’s a tuberculous cavities = tubercle that has liquefied & formed an air-filled cavity –> reactivation or miliary TB
how can you screen for TB?
- tuberculin skin test, Mantoux test, PPD
- intradermal injection of purified protein derivative, check the site in 48-72h, look for CMI
- (+) indicates exposure NOT an active infection necessarily –> type 4 HS rxn
- if the PPD is (+) do a CXR
microscopy/culture for TB
- acid fast stain or fluorescent auramine stain
- Lowenstein-Jensen agar is specific for TB but very slow growth = 6-8 weeks
tx for TB
- combo therapy of 4 drugs = isoniazid, rifampin, ethambutol, pyrazinamide
- initial phase = 2 months followed by 4 months of continuation phase
what do you give for potential exposure
isoniazid treatment
what is the main problem with the length of treatment that you have to do for TB? possible solution to the problem?
- patient noncompliance is a big problem
- you can do DOTS = directly observed treatment short course i.e. someone watches the pt take their meds every day and if they don’t they can be jailed
MDR-TB vs. XDR-TB
- MDR = multidrug resistant = resistant to isoniazid and rifampin
- XDR = extremely drug resistant = resistant to isoniazid, rifampin and at least 1 of the 2nd line drugs
what is the BCG vaccine and why is it not given in the US?
- BCG = Bacille Calmette-Guerin
- live, attenuated M. bovis
- not a high efficacy rate so anyone that gets the vaccine will show a + PPD
- since PPD is what we primarily use to screen in the US if you give the vaccine you lose the effectiveness of your screening test
MAC pneumonia: what are the 2 bugs in the complex
- mycobacterium avium
- mycobacterium intracellulare
characteristics of MAC pneumonia
- weakly gram (+), acid-fast aerobic rods
- mycolic acid in cell wall
- slow growing in culture
- normal inhabitants of soil and water
2 big risk factors for MAC pneumonia
- immunocompromised
2. chronic pulmonary disease
primary vs. secondary MAC pneumonia
- primary = pulmonary infection; similar to TB
- secondary = disseminated infection in ALL organs and bloodstream; seen in AIDS pts w/ low CD4+ T cell counts <50
what is your primary diagnostic tool for MAC?
- acid fast stain
tx for MAC
- resistant to standard TB meds
- use clarithromycin OR azithromycin COMBINED WITH ethambutol AND rifampin
prevention of MAC: who needs it and what do you give?
- give to AIDS pts w/ low T cell counts
- use clarithromycin or azithromycin
characteristics of Nocardia
- gram (+), aerobic
- weakly acid fast
- branching filaments
- normally found in the soil
how is Nocardia transmitted and what are the risk factors?
- transmission = inhalation
- risk factors = imunocompromised and renal transplants
pathogenesis of nocardiosis
- pulmonary infection, lung abscesses
2. spread and form abscesses in brain or kidney
symptoms of nocardiosis
- fever
- night sweats
- malaise
- chest/abd pain
- persistent cough
- anorexia
how can you dx nocardia?
- microscopy = branched long rods
- culture = blood or chocolate agar
tx of nocardiosis?
- IV trimethoprim-sulfamethoxazole
- linezolid
